[idmetro]

DOC;

My understanding is that by reintroducing a certain amount of exhaust gas into the cylinder it not only reduces the emissions by reburning the exhaust gas but it helps moderate the cylinder temperature.

My interpretation of this is that as the engine ages (typically 100K+ miles) and combustion efficiency decreases; you tend to get carbon build up in the cylinder due to ring wear/blowby and if the egr passages get blocked then as the temp in the cylinder climbs the carbon deposits create a hotspot which eventually "burns" the valve. Keeping the egr passages clear and occasionally de-carboning (SeaFoam, GM top cleaner, etc...) will help to avoid these issues.

Anybody else want to add/correct this description?